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than determinate types to M. vitrata damage (Fellow et al., 1977, Lateef and Reed 1981, Saxena et al. 1996). ..... Booker, R. H. (1965). Pests of ... Saxena, K. B., Lateef, S. S, Ariyattne, H. P, Fonseka, H. H. D. and Dharmasena, C. M. D.. (1996).
Morphological and biochemical factors associated with resistance to Maruca vitrata (Geyer) (Lepidoptera: Pyralidae) in short duration pigeonpea V. Sunitha2, G. V. Ranga Rao1, K. Vijaya Lakshmi2, K.B. Saxena1, V. Rameshwar Rao1 and Y.V.R.Reddy1 1 International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, A.P, India 2 Department of Entomology, College of Agriculture, Acharya N G Ranga Agricultural University (ANGRAU), Rajendranagar, Hyderabad 500 030, AP, India

___________________________________________________________________________________ Running title: Factors associated with resistance to Maruca in pigeonpea Corresponding author: GV Ranga Rao, ICRISAT, Patancheru 502 324, Andhra Pradesh, India E-mail: [email protected]

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Morphological and biochemical factors associated with resistance to Maruca vitrata (Geyer) (Lepidoptera: Pyralidae) in short duration pigeonpea V. Sunitha2, G. V. Ranga Rao1, K. Vijaya Lakshmi2, K.B. Saxena1, V. Rameshwar Rao1 and Y.V.R.Reddy1 1 International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, A.P, India 2 Department of Entomology, College of Agriculture, Acharya N G Ranga Agricultural University (ANGRAU), Rajendranagar, Hyderabad 500 030, AP, India

Abstract The spotted pod borer Maruca vitrata is known for its economic importance through out its geographical distribution because of its destructive nature to reproductive parts of several grain legume crops including pigeonpea. Keeping in view the importance of the pest, present studies were carried out on the association of different morpho-chemical traits with resistance/susceptibility to M. vitrata at the International crops research institute for the semiarid tropics (ICRISAT), Patancheru, India. Trichome length, density, sugars, protein and phenols were found to be associated with the resistance to M. vitrata in short duration pigeonpea genotypes. The pod damage by M. vitrata on different short duration pigeonpea genotypes in the field ranged from 5.8 - 68%. Laboratory studies showed less consumption of food and reduced larval and pupal weights of M. vitrata when reared on resistant genotypes (ICPL 98003 and ICPL 98008) indicating the antibiotic effects of the genotypes. Trichome density on upper and lower surfaces of the leaf (390 and 452/9mm2), and length (3.5 mm) and trichome density (442) and length (5.9 mm) on pods were found positively correlated with resistant genotype ICPL 98003. High sugar content in flowers (22%) and pods (10.6%) was responsible for the susceptibility of ICPL 88034, while high phenol concentration in flowers (6.5%) and pods (9.3%) in ICPL 98003 was responsible for resistance. Protein content in pods was highest (25.5%) in susceptible ICPL 88034 compared to resistant ICPL98003 (16.5%). Based on these results, ICPL 98003 was categorized as highly resistant and ICPL 98008 as moderately resistant. This paper discusses the physico-chemical traits associated with resistance to M. vitrata in short duration pigeonpea genotypes. Key words: Pigeonpea, Cajanus cajan, Maruca vitrata, physico-chemical traits, host plant resistance

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Introduction The spotted pod borer Maruca vitrata (Geyer) derives its pre-dominate importance as a pest of tropical grain legumes from its wide geographical distribution, host range and its ability to infest the young growing plant tips, flower buds, flowers, pods and seeds. The destructiveness at critical stages of growth viz, flowering and seed development constitutes a significant constraint to the productivity of grain legumes. During recent years after the introduction of short duration pigeonpea cultivars the damage caused by M. vitrata has been aggravated (Sharma et al., 1999). The yield losses caused by this species in pigeonpea have been estimated to be around $US 30 million annually (ICRISAT 1992) where as Singh (1999) reported 70-80% yield loss in this crop. M. vitrata was controlled primarily through the application of chemical insecticides (Brooker, 1965, Dina 1979, 1988), but total dependence on chemical control may lead to the development of resistance to insecticides, outbreaks of secondary pests and the problem of residues in the food and fodder. Hence the concept of integrated pest management with the emphasis on host plant resistance has gained momentum.

Insect pests are often affected by physico-chemical features of the host plants. Indeterminate type cultivars of pigeonpea possess fewer flowers per cluster than determinate type and hence a disproportionately lower number of pod borer larvae per unit area of reproductive shoots. Studies conducted at ICRISAT and other locations suggested less susceptibility of indeterminate than determinate types to M. vitrata damage (Fellow et al., 1977, Lateef and Reed 1981, Saxena et al. 1996).

The studies conducted by Sharma (1998) showed significant differences in

oviposition preference of M. vitrata under multi-choice conditions. These studies also suggested less suitability of some of the pigeonpea genotypes for growth and development of pod borer under glass house conditions. Thus there is a need for understanding the factors responsible for the resistance to further strengthen the on- going IPM strategies. Hence the present studies were

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undertaken to determine the role of morphological and/or biochemical traits of short duration pigeonpea genotypes associated with resistance to M. vitrata.

Materials and methods

Plant material: Present studies were conducted on three determinate (ICPL 98001, ICPL98002, and ICPL98003) and three indeterminate (ICPL98008, ICPL98012, and ICPL88034) pigeonea genotypes under field, greenhouse and laboratory conditions at ICRISAT, Patancheru, Andhra Pradesh during 2005-06.

Mass rearing of M. vitrata on artificial diet: To obtain required number of larvae at the appropriate developmental stage of the plant, field collected fifth instar larvae were reared in glass troughs measuring 13 x 30 cm on artificial diet following the procedures developed by Ochieng et al. (1981). Pupae obtained were kept in a plastic container for adult emergence and newly emerged adults were released into cages measuring 60 x 30 x 90 cm in size and were fed on 10% sugar solution soaked in cotton swabs. Fresh tender pigeonpea twigs with inflorescences placed in conical flasks filled with water, plugged with cotton were provided as oviposition substrate and the inflorescences were changed daily. The flowers, flower buds and tender leaves were examined for the presence of eggs. The collected egg masses were placed on moist filter paper (Whatman no. 41) kept in Petri plates. After hatching the larvae were released on the artificial diet. The diet was replenished once in two days to provide sufficient food with good sanitation.

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Evaluation of test pigeonpea genotypes for resistance to M. vitrata under field, greenhouse and laboratory conditions:

Field condition: The test genotypes were planted at the ICRISAT, Patancheru research farm during the rainy season 2005. Each cultivar was sown in two rows of each 3m length with a row spacing of 60 cm and 10 cm plant to plant within the row. Each treatment is replicated thrice following randomized block design. Recommended agronomic practices were followed to raise the crop, with a basal application of 100:60:40 kg NPK/ha respectively at the time of sowing. Observations on M. vitrata damage were recorded on ten randomly selected plants in each replicate. From each plant five peduncles were again randomly selected and the pods on the peduncles were examined for M. vitrata damage at the peak infestation when some of the genotypes were completely damaged. Genotypes showing > 60% damage were categorized as susceptible and those showing